206. Reverse Linked List
easyAsked at Goldman SachsReverse a singly linked list iteratively and recursively. Goldman Sachs uses Reverse Linked List as the canonical 'do you understand pointer manipulation' question — they ask for both the iterative and recursive versions in the same round.
By Sam K., Founder, InterviewChamp.AI · Last verified
Source citations
Public interview reports confirming this problem appears in Goldman Sachs loops.
- Glassdoor (2026-Q1)— Goldman Sachs SWE candidate reports list Reverse Linked List as the most-asked linked-list question, often paired with 'now write it recursively'.
- LeetCode Discuss (2025-11)— Reverse Linked List is in the top-10 of LeetCode's Goldman Sachs company tag.
Problem
Given the head of a singly linked list, reverse the list, and return the reversed list. Follow up: A linked list can be reversed either iteratively or recursively. Could you implement both?
Constraints
The number of nodes in the list is the range [0, 5000].-5000 <= Node.val <= 5000
Examples
Example 1
head = [1,2,3,4,5][5,4,3,2,1]Example 2
head = [1,2][2,1]Example 3
head = [][]Approaches
1. Iterative with three pointers (optimal)
Walk the list with prev, cur, next pointers. Reverse each node's next pointer in place.
- Time
- O(n)
- Space
- O(1)
function reverseList(head) {
let prev = null;
let cur = head;
while (cur !== null) {
const next = cur.next;
cur.next = prev;
prev = cur;
cur = next;
}
return prev;
}Tradeoff: O(n) time, O(1) space. The order of operations (capture next BEFORE rewriting cur.next) is the part Goldman is grading — flip the order and the list breaks.
2. Recursive (bottom-up)
Recurse to the end; on the way back up, rewire each node's next pointer to its predecessor.
- Time
- O(n)
- Space
- O(n)
function reverseListRec(head) {
if (head === null || head.next === null) return head;
const newHead = reverseListRec(head.next);
head.next.next = head;
head.next = null;
return newHead;
}Tradeoff: Linear time at O(n) stack space. The 'head.next.next = head' line trips most candidates — it means 'the node after me should now point back to me'. Goldman wants you to verbalize that exact thought.
Goldman Sachs-specific tips
Goldman Sachs interviewers will almost always ask for BOTH the iterative and recursive versions on this one. Show them both even if only one is requested — it signals depth. The capture-next-first detail in the iterative version is what they're grading; reversing the order silently breaks the list and demonstrates you don't understand pointer aliasing.
Common mistakes
- Forgetting to capture the next pointer before rewriting cur.next — leaks the rest of the list.
- Returning head instead of prev in the iterative version — head now points to NULL at end.
- In the recursive version, forgetting head.next = null on the last rewire, which creates a cycle.
Follow-up questions
An interviewer at Goldman Sachs may pivot to one of these next:
- Reverse a subset: reverse nodes from position m to n (Reverse Linked List II, LC #92).
- Reverse in groups of k (LC #25 Reverse Nodes in k-Group).
- Detect a cycle (LC #141 Linked List Cycle) — sometimes asked back-to-back to test pointer fluency.
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FAQ
Which version does Goldman prefer?
Both. Senior interviewers tend to default to iterative because it's O(1) space and clearer for production code; new-grad rounds often start with recursion to test base-case fluency. Be ready with both — they take 2 minutes apiece once warmed up.
What's the most common bug?
Forgetting to capture cur.next before rewriting it. The line 'const next = cur.next' must come BEFORE 'cur.next = prev' — flip them and you immediately lose the tail of the list.
Free learning resources
Curated free links for this problem.